The purpose of this study is to develop a new generation of peptide base vaccine for the prevention of HIV infection. Severe combined immunodeficient (SCID) mice were reconstituted with human peripheral blood leukocytes (hu-PBL-SCID) and separate groups of mice were immunized with tetanus toxoid, Trinitrophenyl-lipopolysaccharide-Brucella abortus conjugate (TNP-LPS-BA), TNP-LPS-E. coli or TNP-Ficoll and sera were tested at several intervals thereafter for specific responses to these antigens. Only tetanus toxoid as a recall antigen was able to induce high titers of specific antibodies in these hu-PBL-SCID mice. In contrast to the expectation, unprimed human cells did not respond to the Brucella abortus LPS conjugate. Therefore hu-PBL of HIV infected donors were transferred into SCID mice and boosted with several peptide conjugates (LPS-BA, KLH) and tested for HIV specific responses. In none of the tested reconstituted SCID mice was a specific HIV response was observed. The mice are currently being investigated for specific cytotoxic (CTL) responses because FACS analyses of hu-PBL-SCID mice indicated that CD4 and CD8 T- cells survive in the peritoneal cavity of these mice. Detection of B-cells in these mice is very difficult although antibody responses, for instance to tetanus, occurs. To improve on the immunogenicity of HIV peptide-LPS-BA conjugates a new set of experiments in normal BALB/c mice was initiated. The HIV peptide is chemically linked to an activated phosphoethanolamine (IAP-PE) incorporated into a liposomal bilayer containing LPS-BA. These liposomes proved to be highly immunogenic and able to induce high titers of HIV neutralizing antibodies. The system will be optimized and in later experiments tested in hu-PBL-SCID mice. In separate experiments, Human Stem Cells were isolated by several procedures from peripheral human blood and cultivated in vitro with interleukins in order to obtain immature/mature B cells which eventually will produce specific antibodies. The sequence of addition of the interleukins was determined: B cells were detected by FACS analyses and immunoglobulin secretion was found by ELISA.